One of the recent commits introduced support for
spice agent-mouse. However, test for this feature
require some tweaking: pass QEMU_CAPS_CHARDEV_SPICEVMC |
QEMU_CAPS_NODEFCONFIG and add "-vga cirrus".

spice agent-mouse support

Usage:
  <graphics type='spice'>
    <mouse mode='client'|'server'/>
  <graphics/>
Signed-off-by: NOsier Yang <jyang@redhat.com>